1. Field of the Invention
The present invention relates to a piezoelectric acoustic component, such as a piezoelectric buzzer or a piezoelectric receiver.
2. Description of the Related Art
Piezoelectric acoustic components, such as piezoelectric buzzers for producing an alarm or operation beep, or piezoelectric receivers, are widely used in, for example, electronic apparatuses, household electrical appliances, and cellular phones.
As described in Japanese Patent Application Laid-Open (kokai) Nos. 7-107593 and 7-203590, such a piezoelectric acoustic component typically has a structure in which a circular metallic plate is bonded to an electrode provided on one major surface of a piezoelectric plate to thereby constitute a unimorph-type vibration body. In such a structure, the vibration body is disposed within a circular housing such that the circumferential edge portion of the metallic plate is supported by the housing and the opening portion of the housing is covered by a cover.
However, use of such a circular vibration body results in poor production efficiency, low acoustic conversion efficiency, and difficulty in implementing a surface-mounting structure. These problems will be described in detail below.
First, production efficiency and acoustic conversion efficiency will be discussed. A process of manufacturing such a piezoelectric acoustic component includes the steps of: forming a circular piezoelectric plate 42 from a green sheet 40 by use of a blanking punch 41 as shown in FIG. 1A; electrically and mechanically bonding a circular metallic plate 43 to an electrode disposed on one major surface of the piezoelectric plate 42 as shown in FIG. 1B; applying a high-voltage direct-current electric field between electrodes located on the opposite main surfaces of the piezoelectric plate 42 for effecting polarization to thereby obtain a vibration body 44; disposing the vibration body 44 within a housing 45; and extending out to the exterior of the housing 45 lead wires 46 and 47 connected respectively to the electrode located on the other major surface of the piezoelectric plate 42 and the metallic plate 43, as shown in FIG. 1C.
However, forming the disc-like piezoelectric plates 42 from the green sheet 40 using a punch as shown in FIG. 1A results in a large portion of the green sheet 40 being unused, resulting in poor material utilization. Since formation of the electrodes and polarization are performed on an individual basis after blanking, processing efficiency is poor. Further, since the blanking punch 41 must be manufactured according to the size of the piezoelectric plate 42, the overall production efficiency is even worse.
As shown in FIG. 2A, since the disc-like vibration body 44 is fixed at a circumferential portion by the housing 45, a maximum displacement point P appears only at the center thereof, so that the volume of displacement is small and the acoustic conversion efficiency is low. As a result, the sound pressure is very low in relation to input energy. Further, since the vibration body 44 is circumferentially restricted, a high frequency is generated. In order to obtain a piezoelectric vibration body of a low frequency, the radius of the vibration body must be increased.
Next, implementation of a surface-mounting structure will be discussed. A piezoelectric acoustic component of a surface-mounting structure is disclosed in, for example, Japanese Utility Model Application Laid-Open (kokai) No. 3-125396. However, this structure has many drawbacks. More specifically, since lead terminals must be integrally formed on the metallic plate, the shape of the metallic plate becomes complicated. Also, the shape of the housing becomes complicated because of the need to extend the lead terminals out from the housing. Further, since the lead terminals are brought into contact with or are fixedly attached to the piezoelectric plate, a load is apt to be exerted on the piezoelectric plate. Therefore, implementation of such a piezoelectric acoustic component of a surface-mounting structure is inferior because of the poor reliability and the high cost of manufacture.